As an important field effect transistor, a thin film transistor is widely used in a technical field of display. As illustrated in FIG. 1, the thin film transistor mainly includes a gate electrode 10, a gate insulating layer 20, an active layer 30, an etch barrier layer 40, a source electrode 50 and a drain electrode 60. Copper may be selected as an electrode material for forming the source electrode 50 and the drain electrode 60, and a thin film transistor thus formed has an advantage of good conductivity.
Since the copper has certain diffusibility, when the thin film transistor is turned on, the copper will diffuse into the active layer, affecting conductivity of the active layer. Therefore, in the prior art, the copper is not used alone, but a multi-layer structure is used. For example, at least a diffusion blocking layer and a copper layer are included, wherein, the blocking layer is usually made of molybdenum niobium (MoNb), for blocking the copper from diffusing into the active layer.
However, inventors found that the prior art at least has problems as follows: the thicker the diffusion blocking layer is, the better the effect of blocking the copper from diffusing into the active layer is; but manufacturers have strict requirements on cost and thickness of a device, so it is not possible to make the diffusion blocking layer too thick. Meanwhile, in order to improve performance of the device, after forming a thin film transistor, an annealing process will be performed thereon; the annealing process needs to be implemented in a high temperature environment, and the copper diffuses aggressively at high temperature. The diffusion blocking layer is poor in preventing the copper from diffusing due to these two reasons, further affecting conductivity of the active layer, thereby affecting performance of the thin film transistor.